1. Field of the Invention
The present invention relates to a hub apparatus that multiplexes packets input via plural input ports and transmits the multiplexed packets to a network.
2. Description of the Related Art
A hub apparatus that concentrates packet data transmitted from plural users is generally arranged at the input/output of a network such as a carrier network.
FIG. 1 is a diagram showing an exemplary configuration of a conventional hub apparatus. The illustrated hub apparatus includes a policer unit 11, a packet multiplexer 12, a shared memory 13, and a shaper 14. The policer unit 11 is configured to monitor the input bandwidth and includes policers 11P1-11Pn having input token buckets that are assigned to input ports 101-10n, respectively. When packet data are input at intervals exceeding the MBS (Maximum Burst Size) for the input token buckets, that is, when burst packet data are input, some packet data are discarded to control the traffic of input packet data.
The packet multiplexer 12 multiplexes packet data acquired (i.e., not discarded) by the policer unit 11 according to header information and stores the multiplexed packet data in the shared memory 13. The shaper 14 includes an output token bucket that accumulates tokens, reads transmission packet data from the shared memory 13 when tokens for transmitting the transmission packet data are accumulated in the output token bucket, and transmits the packet data to a network via a single output port 15 at equal packet transmission intervals in order to reduce data bursts at the hub apparatus.
It is noted that tokens indicate the ability of the policer unit 11 and the shaper 14 to transmit packet data. According to the token bucket scheme employed by the policer unit 11 and the shaper 14 in the present example, tokens are accumulated in a token bucket at a fixed rate, and when a predetermined amount of tokens are accumulated, received packet data are transmitted and a corresponding amount of tokens are consumed from the token bucket. When the tokens accumulated in the token bucket exceed the MBS for the token bucket, surplus tokens exceeding the MBS are discarded.
Japanese Laid-Open Patent Publication No. 4-178044 discloses a traffic control scheme for accurately determining whether service quality of call parameters requested by the user may be ensured upon accepting a call and maintaining the service quality at a maximum during switching operations of the accepted call.
Japanese Laid-Open Patent Publication No. 5-227193 discloses a technique for improving throughput of an output circuit while individually satisfying requested communication qualities for information signals of various service classes by taking into consideration the differences in traffic characteristics of the information signals of different service classes, statistical multiplexing effects, and fluctuations in burst characteristics, for example.
Japanese Laid-Open Patent Publication No. 6-46085 discloses a technique for generating traffic parameters of every call channel based on the transmission cell count number of every time interval and controlling a policing circuit based on the generated traffic parameters.
The illustrated hub apparatus of FIG. 1 performs packet data traffic monitoring by having the policer unit 11 and the shaper 14 perform token monitoring independently. In this case, when burst packet data are momentarily input, packet data may be discarded at the policer unit 11 side even when there are sufficient resources (output tokens) at the shaper 14 side, for example.
It is noted that in variable length packet data communication, one port of a hub apparatus is shared by plural users, and therefore, when plural users simultaneously establish communication for different services, packet data may be concentrated, communication packet intervals may be shortened, and the input bandwidth may be occupied so that the bandwidth of input packet data may momentarily increase. Such packet data are referred to as burst packet data.
FIG. 2 is a diagram illustrating the increase/decrease of policer tokens at a given port and the acquisition of input packet data. The policer unit 11 may enable acquisition of input packet data when sufficient tokens for acquiring the packet data are accumulated. By acquiring the packet data, a corresponding amount of tokens are consumed.
As is shown in FIG. 2, the intervals between input packet data P1 through P3 are relatively long so that sufficient time may be secured for accumulating tokens necessary for acquiring the packet data P1 through P3. Thus, the packet data P1 through P3 may be accurately acquired.
On the other hand, intervals between input packet data P4 through P6 are rather short (burst packet data) so that sufficient time may not be secured for accumulating tokens for acquiring the packet data P4 through P6, and tokens may be consumed without being sufficiently replenished. Thus, tokens may be depleted and packet data P6 may have to be discarded as a result.